CHEVY CHASE -- The patrol car with Officer Reinhold Springirth was stationed on Newlands Street recently in full view of traffic whizzing along Connecticut Avenue. Spotting the cruiser, more than a few motorists tapped their brakes to comply with the speed limit of 30 mph.

"We have a lot of traffic problems here," said George Winkel, chief of the Chevy Chase Village Police Department, watching Springirth at work.

"But Reinhold helps a lot, providing a very real patrol presence. He works 24 hours a day, and we don't have to pay him overtime or benefits," Winkel said.

In the 2 1/2 years he has worked for Chevy Chase Village, an affluent area of 715 homes just outside northwest Washington, Springirth has become a steady fixture in local law-enforcement efforts.

Literally. Springirth is a mannequin.

"Don't call him a dummy," Winkel said sternly. "He takes exception."

Posing a mannequin as a police officer, complete with cap and sunglasses, is a crime-fighting ploy used at times in places other than Chevy Chase Village, New York state, New Jersey and Connecticut. Winkel himself has used the tactic for years.

After retiring from the U.S. Park Police in the early 1980s, Winkel served as police chief in Herndon, Va., a growing community west of Washington, and later in Old Orchard Beach, Maine, posing mannequins in both places.

Taking over as chief here in late 1994, he reprised the idea and named the mannequin after the first night watchman hired by the village in the 1920s, Reinhold Springirth. By Winkel's research, the original Springirth was a native German who also served as the village garbage collector.

These days, the local police force has grown to 10 people with five cars, one of which is used to position Springirth to deter speeders or, often at night, to deter crime. Winkel said he thought that a recent drop in car break-ins was due, in part, to a patrol car parked on a neighborhood street with Officer Springirth positioned at the wheel.

"We had 16 cars broken into over five weeks in February and March," Winkel said. "We are starting putting Reinhold in the area from 2 to 5 a.m. and we haven't had any break-ins since March 8."

But the greater effect is probably on speeders.

Springirth is generally posted on village streets to slow traffic and often, a live officer is lurking a block or two away with a speed detection device.

In any case, Winkel said, traffic accidents along Connecticut Avenue, a major six-lane route connecting Washington and the Beltway, are declining. In Springirth's second full year on the job, 1996, the number of accidents fell to 157 from 175 in 1995.

Gerald Arenberg, a spokesman for the National Association of Chiefs of Police, said that in his 40-year career in law enforcement he heard "from time to time" of departments' using mannequins to slow traffic and deter crime. As one example, the Maryland State Police in recent years have placed "illusion cars," vehicles sawed in half lengthwise, along highways to slow speeders.